1. Field of the Invention
The present invention relates to lithium secondary cells and methods for preparing active materials for negative electrodes for the lithium secondary cells.
2. Discussion of Background
With rapid progress of electronic technology in recent years, trend for small sizes and light weights of electronic appliances is remarkable, and expectation for cells as their power sources is likewise high. Namely, there is substantial expectation for cells provided with excellent storage stability as well as high energy density with small sizes and light weights.
As the most prospective cell system to satisfy such expectation, a research has been active for developing lithium cells wherein lithium is used as the negative electrode. By virtue of their excellent properties, lithium secondary cells have been rapidly put on market as portable power sources for e.g. VTR cameras, portable telephones or personal computers. However, such cells usually have a difficulty that no adequate charge-discharge cycle life can be obtained.
Therefore, it has been proposed to use, as negative electrode materials, carbon-lithium intercalation compounds having lithium ions intercalated to various carbon materials, and various carbon materials suitable for this purpose have been studied.
For example, it has been proposed to use, as a negative electrode material, graphite such as natural graphite, or a carbon material prepared by baking various resins or pitches. However, a further improvement in the cell performance is still desired to make it applicable to a large size cell useful for a so-called dispersion type power storage system such as a system for domestic power storage at night or for electric vehicle.